The present invention relates to manufacturing parts out of reinforced plastics material, in particular structural parts for motor vehicles.
It is known for sheets of fibers impregnated in thermoplastic material, to be used in particular to make the bumper beams of motor vehicles.
By way of example, such sheets are known under the names TRE or TWINTEX.
TRE (Thermoplastique Renforcxc3xa9 Estampable [stampable reinforced thermoplastic]) is constituted by polypropylene reinforced with glass fibers.
TWINTEX (trademark registered by Vetrotex) is a fabric of yarns constituted by glass fibers embedded in polypropylene.
TEPEX (trademark registered by Du Pont de Nemours) is a drapable thermoplastic material having continuous fibers, like TWINTEX.
It is also known to use multilayer sheets obtained by superposing plies of TRE and plies of the TWINTEX or TEPEX type.
Such sheets need to be heated in order to be shaped.
International patent application WO 98/52793 discloses a method of manufacturing structural parts in which a sheet comprising reinforcing fibers impregnated in thermoplastic material are initially placed in an open mold, after which the mold is closed, and thermoplastic material is injected into the mold under pressure.
There exists a need to integrate local reinforcement into such a structural part, for example in order to improve the mechanical strength of certain zones.
In above-mentioned international application WO 98/52793, local reinforcement is held captive between two outer sheets, thereby complicating manufacture and making it necessary to use more than one sheet.
The present invention seeks to facilitate manufacturing a structural part out of one or more sheets comprising fibers impregnated in thermoplastic material, e.g. sheets of TWINTEX or any other similar material.
The invention achieves this by the fact that:
at least one sheet and local reinforcement are superposed in a mold before the mold is closed, with at least one of the sheet and the local reinforcement being constituted by reinforcing fibers and thermoplastic material, the mold having a setback beside the local reinforcement and of larger dimensions than the local reinforcement; and
thermoplastic material is then introduced into the setback so as to establish pressure therein serving to compact the local reinforcement and underlying region of the sheet, the mold being shaped so as to compress the sheet on either side of the local reinforcement during closure of the mold.
By means of the invention, it is relatively easy to put local reinforcement into place since there is no need for the or each piece of local reinforcement to be positioned very accurately in the mold.
In the invention, the above-mentioned setback is not intended to act directly to apply the pressure that is needed to compact the fibers of the local reinforcement and/or of the underlying region of the sheet, this pressure being obtained by means of the plastics material that is put into place prior to closing the mold in register with the setback or that is injected into the setback after the mold has been closed.
If, on the contrary, the pressure required for compacting has to be obtained directly by clamping the local reinforcement between the two mold portions on closure, then it would be necessary for the local reinforcement to be positioned very accurately, and that would lead to difficulties.
In a particular implementation of the invention, the sheet and/or the local reinforcement, and preferably both of them, are made of a fabric of yarn constituted by glass fibers and thermoplastic material, of the TWINTEX type.
The thermoplastic material is preferably introduced into the setback associated with the local reinforcement by pressure injection after the mold has been closed.
In a variant, the thermoplastic material is introduced into the setback before the mold is closed, and it is closure of the mold which produces the pressure required within the setback to compact the local reinforcement and the underlying sheet.
The depth of the setback is preferably slightly greater than the thickness of the local reinforcement.
Advantageously, the sheet is caused to project out from the mold, and after the mold has been closed, the portions of the sheet which project therefrom are then trimmed off.
Thus, the sheet can be positioned within the mold without too many constraints.
The invention also provides a reinforced plastics material part obtained by implementing the method as defined above.
The invention also provides a reinforced thermoplastic material part characterized by the fact that it comprises a non-plane sheet of a fabric of yarn constituted by reinforcing fibers and thermoplastic material, the sheet being locally lined with local reinforcement on which there is overmolded a mass of thermoplastic material that overflows slightly onto the sheet on either side of the local reinforcement.